Electrical condenser



March 20, 1962 A. J. RUSCITO 3,026,457

ELECTRICAL CONDENSER Original Filed Sept. 28. 1951 7 15M flq-LpjINVENTOR ATTORNEY M M :2) W

A Unite f States Fatent 3,026,457 ELECTRICAL CONDENSER Anthony J.Rnscito, Unadilla, N.Y., assignor to The Bendix Corporation, acorporation of Delaware Original application Sept. 28, 1951, Ser. No.248,698, new

Patent No. 2,951,002, dated Aug. 30, 1960. Divided and this applicationJune 4, 1958, Ser. No. 741,709 g 3 Claims. (Cl. 317-260) This inventionrelates to electrical apparatus and more particularly to electricalcondensers or capacitors and methods for fabricating the same.

This is a divisional application based upon application Serial No.248,698, filed September 28, 1951, for Electrical Condenser and Methodof Making Same, and now Patent No. 2,951,002. a

One of the objects of the present invention is to provide -a novellyconstructed electrical condenser which has better physical andelectrical characteristics and properties than condensers heretoforemade of the same or equivalent materials.

Another object is to provide a novel spirally wound condenser of thetype embodying foil sheets separated by sheet insulation, such as paper.

A further object is to provide a novel electrical condenser which hashigher capacity and is capable of withstanding higher temperatures andvoltages than prior known condensers of the same size and weight.

Still another object is to provide a condenser which is novelly soconstructed and shaped that a plurality thereof may be installed in aminimum of space for connection in the same or different electricalcircuits.

A still further object is to provide a condenser wherein the terminalsfor the plates thereof are incorporated in the structure in a novel andsimplified manner.

Another object is to provide a novel, high quality condenser and a novelmethod of making the same at relatively low cost.

The above and further objects and novel features of the invention willmore fully appear from the following detail description when the same isread in connection with the accompanying drawings. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration only and are not intended as a definition of the limits ofthe invention.

In the drawings, wherein like reference characters refer to like partsthroughout the several views,

FIG. 1 is an end view illustrating a condenser or capacitor in theprocess of being wound;

FIG. 2 is a side view of a partially wound condenser;

FIG. 3 is an end View of one form of a finished condenser embodying andmade in accordance with the present invention;

FIG. 4 is a side view of a fixture adapted for use in making condensersin accordance with the invention.

The so-oalled condenser or capacitor discharge type of ignition systemfor combustion engines has come into quite common use in recent years,particularly on socalled jet or gas turbine engines for aircraft where ahigh energy spark is required. In these systems a condenser isrepeatedly charged and discharged to create the necessary ignitionsparks having high energy. Accordingly, the condenser is an essentialpart of such ignition sys tems and failure thereof is likely to resultin faiilure of the engine and consequent loss of life or severe injuryto personnel and destruction of valuable aircraft or other property. Itis therefore an important object of this invention to improve thisessential element of the presentday ignition system-s by making the samemore efficient.

and more durable under most severe operating conditions. The embodimentof the invention illustrated in the drawings and hereafter described indetail, by way of ice example only, is a condenser having a capacity ofone microfarad and adapted for use as a storage condenser in an engineignition system. The conductive plates of the condenser are constitutedby two strips 10 and 11 of thin metal foil. Aluminum foil having athickness of about .00025 inch has been found satisfactory in onecommercial embodiment. These strips are preferably of equal width andare spirally wound directly over each other but separated and insulatedfrom each other by two layers 14 and 15 of suitable insulating material,such as paper, each layer as shown in the exemplary embodimentcomprising three sheets. Each insulating sheet is preferably of hardcalendered kraft paper stock about .0003 inch thick and sufl'icientlywide to extend about .025 inch beyond both edges of the foil sheets 10and 11, but other known forms of sheet insulation may be used. The foilsheets are preferably longitudinally offset about a half inch so theadjacent ends thereof will be staggered in a like amount. The foilsheets are, of course, insulated from each other throughout byinsulating layers 14 and 15 and a few of the outermost turns arepreferably free of foil.

Terminals 16 and 17 preferably extend from laterally opposed halves andopposed ends of the condenser. Said terminals may consist of thin stripsof metal, one in contact with one foil plate 10 and the other in contactwith foil plate 11. The terminal strips may be loosely inserted in thepositions shown when the condenser has been approximately half wound.When the condenser has been impregnated and compressed in the novelmanner hereinafter described, the terminals will make excellent contactwith the foil layers and be well secured in position without the use ofsolder or the like. The wound layers of foil and insulating sheets areimpregnated and retained in a substantially flat or out-of-round shapeby an insulating compound which is applied in a manner to be hereinafterdescribed. The layers of foil and insulating paper are tightlycompressed to a flat shape (FIG. 3) with the compound filling the poresand interstices in the paper layers, thereby improving the insulatingproperties thereof. The paper layers are not stressed by the action ofthe impregnating compound and the density thereof is renderedsubstantially greater by compression than it was before fabrication ofthe condenser.

The novel method comprehended by this invention for fabricating acondenser of the above description includes tightly winding the foillayers 10 and 11 and paper or other insulating layers 14 and 15 on afiat, highly polished mandrel 18, as illustrated in FIG. 1. Tofacilitate removal of the mandrel after the winding of the con denser,the edges of the mandre may be very slightly tapered, such as to theextent of about .001 inch per inch of length. When winding the twolayers of foil and two triple layers of insulation so that there is alayer of insulation between the foil strips at all points, care shouldbe taken to avoid any wrinkles. When about half the length of the paperand foil strips have been wound, the terminal strips 16 and 17 areinserted in the positions illustrated. These leads or terminals shouldbe smooth and free of burrs and the paper and foil strips should beclean and free of any particles which might rupture the paper or foilunder compression. The winding should be carried out in a room free fromdust or similar particles of foreign matter in the air. When the desirednumber of turns have been wound, the foil layers are cut With theadjacent ends thereof staggered about a half inch or more and at leastthe outside paper is wound to completely cover the outside foil andsecured with a minimum of adhesive compound to prevent unwinding of theturns during further fabrication.

The condenser is now slipped off the mandrel so that when the sidesthereof are lightly pressed toward each other to close the opening leftby the mandrel, the layers: of foil and paper will assume a looselywound condition. The loosely wound condenser C is now supportedbetween'two flat, smooth plates or spacers 19 of fluorine polymer or theequivalent, each large enough to protrude beyond the condenser on allfour sides. The plates should be clean and free from nicks, mars or anycontamination and made of a material to which the impregnating compoundwill not adhere. If desired, a plurality of condensers C may be stackedone above the other in a suitable fixture 20 with a supporting plate 19between each pair. The plates 19 are initially individually supported insomewhat wider spaced relation to each other than is illustrated in FIG.4, in any suitable manner, such as by notched standards that removablycooperate with fixture 20 but are not shown in the drawing. Thesecondensers, thus loosely stacked or supported, are dried in a convectionoven or the like at about 190 F. for about hours or more and at aboutthe same temperature forabout 24 hours or more in an impregnating tankor charnber evacuated to about one-half inch of mercury absolute:pressure or less.

The condensers are now ready for impregnation with a. suitableinsulating compound which may be applied in liquid or viscous form andthen permitted or caused to set to a relatively rigid or yieldable form.One suitable: compound of the many which may be used for this purposecomprises about 18.5 parts by weight of styrenemonomer, 81.5 parts of acasting resin, such as Rohm and Haas Company Paraplex P-13 whichconsists of equal! parts of styrene monomer and polyester monomer, and 3parts of a catalyst, such as lauroyl peroxide, a suitable form thereofbeing commercially known as Lucidofi Alperox C. The catalyst speeds upthe polymerization of. the castingresin. V

Impregnation of the condensers may be effected in the vacuum chamber inwhich the condensers are dried, preferably while said chamber isevacuated .to about one-halff inch of mercury absolute pressure or, lessafter the fixture supporting the condensers has cooled to atemperaturebelow about80 F. Cooling of the chamber and fixture may be effected inany suitable manner, such as by circulating a coolant in the heatingcoils. The dried. condensers may be moved from the drying oven to a.

' diflerent impregnating chamber but this is not preferable. Theevacuated impregnating chamber, when cooled, is flooded with theimpregnating compound which is in liquid or viscous form at atemperature between approximately 45 F. and 70 F. The compound beforebeing introduced into the impregnating chamber is preferably stirredunder vacuum for the purpose of removing air and other gases therefrom.

After the loosely wound condensers have been thus thoroughly saturated,the same are removed from the impregnating chamber and'placed underspring or gaseous type pressure of about 50 to 100 lbs. per square inch.The pressure is applied to the end-most separating or supporting platesand for best results should be applied gradually in increments over aperiod of about 15 minutes to permit suitable flow of the impregnatingcompound and avoid undesirable stresses of the layers. This gradualapplication of pressure forces excess compound from between the layersof the condensers and insures the absence of air or vapor bubbles.Additionally, the compound is pressed into the pores or interstices ofthe matedenser and to improve its other electrical and physicalcharacteristics and properties. It may be desirable to support thecondensers for a few minutes in such a position as to permit excesscompound to drain from the ends of the coils, i.e., from between theprojecting edges of the paper insulating layers which are not under fullcompression.

When fixture 20 is used, the initial pressure for compressing thecondensers to remove excess compound and effect other advantageousresults herein mentioned may be applied mechanically, hydraulically orin any other suitable manner to yoke 21 and thence through a coil spring22 to a pressure plate 23 slidably supported in the fixture and engaginguppermost plate 19. When the desired pressure has been graduallyattained, the spring 22 is maintained under compression between yoke 21and plate 23 by stop clips 24 which extend into slots in pins 25 andengage the lower face of fixed plate 26. The pins 25 may be adjusted tothe proper vertical position by nuts 27 before the downward pressure onyoke 21 is released. It Will be understood that if supports or standardsare used for spacing plates 19 during the drying process, the same mustbe removed before the compression pressure is applied so that eachcondenser Will be pressed between two plates 19.

While thus held under compression by spring 22 or some other suitableform of expanding pressure, the compressed condensers are preferablybaked to accelerate polymerization or setting of the remainingimpregnating compound. When a compound of the nature described above isused, baking may be at a temperature of about 169 F. to 180 F. for about14 to 16 hours during which time the spring or other pressure shouldpreferably not be permitted to decrease appreciably. This result may beeffected by properly designing the spring in the light. of the furthercompression of the condensers which results from the shrinkage of thecompound and compression of the paper during the baking and hence,drying and setting process. The continuous application of pressureduring the setting of the compound avoids the creation of physicalstresses in and possible rupture of the insulating layers which are aptto otherwise result r from the contraction of the compound and from theunrials making up the condenser and compresses to beyond its originalstate of density the paper insulating layers which may have beenswollenor'expanded by the liquid impregnating compound. The pressurealso removes the.

tween the paper and foil strips, is also insured thereby V bringingfthecondenser plates 10, 11. as close together as possible in order toincrease the capacity of the coneven curing and cooling which resultsfrom inability to heat and cool all of the layers uniformly. The outsidelayers cure and cool before the inside layers, and without the aid ofthe external pressure the inside layers wound tend to pull away from theouter layers, causing irreparable damage or stresses which reduce theresist- :mce of the insulation to electrical breakdowns or rup- .ure.

After baking, the condensers are permitted to cool to room temperatureunder continued pressure of spring 22. The same are then removed fromthe fixture and any compound on the exposed ends of terminals 16, 17 iscleaned off with a suitable solvent. The condensers are now ready foruse and for best results should be housed 1n a moisture tight casing orcoating.

There is thus provided a novelly constructed electrical condenser orcapacitor in the form of a solid and dense mass which is entirely freeof internal voids or air pockets and. wherein the layers are free ofdetrimental internal stresses. Said condenser is capable of withstandinghigher temperatures and higher voltages than heretofore known condensersof comparable size and weight and has higher insulation. resistance thanany previously known condenser of comparable capacity. In

comparison to known structures, said condenser permits less electricallosses, possesses a better power factor and has less corona. Theinvention also comprehends a novel method for making condensers to endowthem with the above advantages. Condensers made in accordance with saidmethod are extremely reliable and will of condensers adapted for thesame purposes and uses. Said condensers are physically durable as wellaselectrically superior.

Although only a limited number of embodiments of or variations in thecondenser and method comprehended by the invention have been illustratedin the drawings and described in the foregoing specification, it is tobe expressly understood that the invention is not so limited. Variouschanges and modifications which do not depart from the spirit and scopeof the invention will now be apparent to those skilled in the art.

What is claimed is:

1. An electrical condenser comprising at least two layers of sheetmetal, at least two layers of sheet insulation, said layers beingspirally wound with the metal layers separated by said insulatinglayers, and opposed halves of the condenser as divided by a planecontaining the Winding axis thereof being compressed and pressedtogether to form a substantially fiat condenser having substantiallyparallel plane sides joined by substantially semi-circular sides withthe adjacent surfaces of adjacent layers in substantial face-to-faceengagement, and a solid heat-set synthetic resin compound impregnatingsaid layers and filling the spaces which remain in and between saidadjacent engaging surfaces when said layers are subjected to compressivepressure while the compound is flowable and during the setting thereof.

2. A substantially fiat, spirally wound condenser comprising at leasttwo layers of sheet metal separated by layers of sheet insulation andhaving the opposed halves of the innermost turn of said insulation inengagement with each other, said condenser being compressed so thatadjacent layers thereof are in close surface-to-surface engagement witheach other, and a solidified thermosetting insulating compound of thetype adapted to solidify from a flowable state impregnating said layersand filling the spaces which remain in and between the engaged surfacesof said layers when the condenser is continuous 1y subjected tocompressive pressure during the solidification of said compound by theapplication of heat.

3. An electrical condenser as defined in claim 2 Wherein theimpregnating compound is a synthetic resin which is adapted to shrinkupon solidification and which is solidified by the application of heatduring the applica tion of compressive pressure to the condenser.

References Cited in the file of this patent UNITED STATES PATENTS719,973 Wotton Feb. 3, 1903 774,115 Splitdorf Nov. 1, 1904 1,706,816Pickard Mar. 26, 1929 1,726,343 Danziger Aug. 27, 1929 1,746,469 GrunowFeb. 11, 1930 1,829,015 Reiher Oct. 27, 1931 1,842,648 Bartel Jan. 26,1932 2,014,399 Sprague Sept. 17, 1935 2,107,780 Danziger Feb. 8, 19382,256,160 Britton Sept. 16, 1941 2,303,283 Kirkwood et al Nov. 24, 19422,325,531 Mertens July 27, 1943 2,495,167 Horstman et al Jan. 17, 19502,506,026 Kifer et al. May 2, 1950 2,534,994 Scott et al. Dec. 19, 19502,634,315 Allison Apr. 7, 1953 2,665,400 Walker Jan. 5, 1954 2,738,453Robinson Mar. 13, 1956 FOREIGN PATENTS 416,735 Great Britain Sept. 20,1934 OTHER REFERENCES Davidson: An Abstract of Application No. 65,722,filed December 16, 1948, and published May 22, 1951, in 0.6., vol. 646,page 1378.

1. AN ELECTRICAL CONDENSER COMPRISING AT LEAST TWO LAYERS OF SHEETMETAL, AT LEAST TWO LAYERS OF SHEET INSULATION, SAID LAYERS BEINGSPIRALLY WOUND WITH THE METAL LAYERS SEPARATED BY SAID INSULATINGLAYERS, AND OPPOSED HALVES OF THE CONDENSER AS DIVIDED BY A PLANECONTAINING THE WINDING AXIS THEREOF BEING COMPRESSED AND PRESSEDTOGETHER TO FORM A SUBSTANTIALLY FLAT CONDENSER HAVING SUB-